Babies that have big appetites are usually seen as a healthy sign, but scientists say it may indicate they are more predisposed to obesity later on in life.
Infants that display two key aspects of appetite grow unusually rapidly up to the age of 15 months, research has shown.
This potentially increases their chances of becoming obese children, according to experts.
A second study found that 10-year-olds with a lower satiety response, making them less likely to stop eating when they feel full, were genetically more susceptible to obesity.
Satiety responsiveness (SR) was one of the measurements taken to monitor appetite in infants.
Scientists studied data from non-identical same sex twins born in the UK in 2007 who had different levels of SR and food responsiveness (FR), the urge to eat when seeing or smelling tempting food.
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Within pairs, the baby that was more food responsive or less satiety responsive than its twin grew faster.
At 15 months old, both traits separately caused a twin to be around two pounds heavier than its sibling.
Lead scientist Professor Jane Wardle, from the Health Behaviour Research Centre at University College London, said: "Obesity is a major issue in child health.
"Identifying factors that promote or protect against weight gain could help identify targets for obesity intervention and prevention in future. These findings are extremely powerful because we were comparing children of the same age and same sex growing up in the same family in order to reveal the role that appetite plays in infant growth.
"It might make life easy to have a baby with a hearty appetite, but as she grows up, parents may need to be alert for tendencies to be somewhat over-responsive to food cues in the environment, or somewhat unresponsive to fullness. This behaviour could put her at risk of gaining weight faster than is good for her."
The findings appear in the journal JAMA Pediatrics alongside a second study by another UCL team from the Health Behaviour Research Centre.
Genetic data from 2,258 children aged 10 were used to create scores for susceptibility to obesity. The "polygenic obesity risk" (PRS) ratings were based on the number of high-risk variants among 28 obesity-related genes in each child.
"As expected, we found that children with a higher PRS score were likely to have larger BMI (body mass index) and waist circumference," said Dr Clare Llewellyn, who led the research. "But more importantly, we also found that these children were more likely to have low satiety responsiveness.
"This suggests that satiety responsiveness could be targeted for pharmacological and behavioural interventions, to prevent or treat obesity.
"For example, children with lower satiety sensitivity could be taught techniques that might improve their fullness signals when eating, such as slowing their eating speed. Another approach might be to provide better advice to parents and children about appropriate portion sizes, limiting access to 'second helpings' and ensuring tempting treats are out of sight between meals."